1. Field of the Invention
The present invention is generally related to controller/drivers and display device including the same, more particularly, to controller/drivers adapted to color reduction.
2. Description of the Related Art
Controller/drivers are used for driving display panels, including liquid crystal display panes. Controller/drivers may be mechanically separated from the display panel, or integrated on the display panel typically using a chip-on-glass (COG) technique.
Controller/drivers are desired to display high quality images on the display panels. Such requirement may be satisfied by using a display panel adapted to an increased number of colors, and a controller/driver adapted to pixel data composed of increased data bits for each pixel.
However, this approach is not suitable for controller/drivers and display panels disposed within portable devices, including cell phones and PDAs (personal data assistant), because various technical limits are imposed on such controller/drivers and display panels. One requirement imposed on controller/drivers and display panels for portable devices is reduction in power consumption, and another is reduction in mounting space. In order to reduce power consumption, display panels for portable devices, especially LCDs, are not allowed to display an increased number of colors. Additionally, it is undesirable for controller/drivers within portable devices to include a display memory having an increased capacity for storing increased pixel data, from the viewpoint of power consumption and mounting space. Therefore, controller/drivers within portable devices require special techniques for achieving high quality images.
Japanese Open Laid Patent Application No. P2002-287709 discloses a controller driver suitable for portable devices, which achieves displaying high quality images. The disclosed controller/driver is composed of a circuit for color reduction based on dithering or error diffusion. Such architecture allows the controller/driver to display high quality images using a display memory with a reduced capacity.
Recently, however, user's requirements include further improvement in image quality, and therefore conventional color reduction based on dithering and error diffusion does not satisfy such user's requirements. Users of portable devices now desire to display photograph images on the display, and this necessitates considerably high image quality. Nevertheless, color reduction based on conventional dithering suffers from granular noise, while color reduction based on conventional error diffusion suffers from unpleasant moiré patterns. Therefore, there is a need for providing a controller driver which achieves sophisticated color reduction for improving image quality.
Additionally, controller/drivers are desired to be multifunctional. When a portable device is installed with multiple LCDs, the LCDs are desirably driven by using a single controller/driver. Driving multiple LCDs with a single controller/driver effectively simplifies the routing of the wirings within the portable device.
In another aspect, controller/drivers are desirably adapted to various image formats other than the bitmap format. One drawback of the bitmap format is large data size, and this drawback is serious for controller/drivers for portable devices. Receiving image data with increased data size undesirably increases power consumption of controller/drivers, because controller/drivers require power for receiving data bits. One approach for solving this drawback is transferring images with an image form other than the bitmap form, which allows reduction in the image data size. For example, transferring images with the vector form or the JPEG form is a promising technique for reducing power consumption of controller/drivers. It should be noted that, to the inventors' knowledge, no prior art discloses a display device which transfers images to a controller/driver using an image format other than the bitmap form.
These requirements are desirably satisfied along with the reduction in the power consumption and mounting space, including the reduction in the capacity of the display memory incorporated within the controller/driver. Therefore, there is a need for providing a multifunctional controller/driver which achieves high quality images along with the reduction in the display memory capacity.